In recent years, to support user works, a study relating to a so-called Augmented Reality (AR) in which various information is superimposed and displayed on an image taken by a camera has been conducted (for example, see Ishii et al., “Proposal and Evaluation of Decommissioning Support Method of Nuclear Power Plants using Augmented Reality”, Transactions of the Virtual Reality Society of Japan, 13(2), pp. 289-300, June 2008).
In a system that implements the AR, in order that information be superimposed on a suitable position on an image taken by a camera, it is requested that a virtual space is accurately aligned to a real space. For that purpose, it is requested that a position and an orientation of the camera in the real space may be accurately grasped. Therefore, proposed is a technique to estimate a position and an orientation of the camera from a position and a shape of a known marker installed in advance on the image (see, for example, Kato et al., “An Augmented Reality System and its Calibration based on Marker Tracking”, Transactions of the Virtual Reality Society of Japan, 4(4), pp. 607-616, December 1999).
However, it is difficult to accurately detect a marker on the image in some cases depending on photographed conditions. Moreover, a marker comes off from a photographed range of the camera, and as a result, the marker is not picked up on the image in some cases. In such a case, it is difficult to estimate an orientation of the camera based on the marker. Therefore, proposed is a technique to estimate a position and an orientation of the camera based on multiple feature points extracted from a photographed image (see, for example, Japanese Laid-open Patent Publication No. 2005-326274).